The present invention relates to artificial hearts.
Numerous types of artificial hearts have been proposed which serve to assist or completely replace a defective heart.
However, hitherto none of these known artificial hearts has given entire satisfaction through being unable to satisfy the very stringent requirements which must be fulfilled without any possibility of failure.
Reference is made in this connection to the work "Artificial Heart" written by Tetouko Akutsu M.D., Ph.D. and published in 1975 by Igaku Shoin Ltd., Tokyo and by Excerpta Medica, Amsterdam. Reference can also be made to the article "Mechanically Assisted Circulation, the Status of the NHLBI Programme and Recommendations for the Future"which appeared in Volume 1, No. 2 of November 77 of Artificial Organs published by International Society for Artificial Organs, Suite 400 - 10300 Carnegie Avenue, Cleveland, Ohio 44106, U.S.A.
The above two documents contain recent studies of all hitherto known artificial heart types and the conditions which must be fulfilled by these hearts.
A first condition which an implantable artificial heart must satisfy is that its overall dimensions must be sufficiently small to enable it to be implanted and supported by the patient without leading to rejection phenomena and without constituting a too restricting discomfort. This condition will be fulfilled if the dimensions and volumes ejected during each cycle of the artificial heart are of the same order as the dimensions and average systolic ejection volume of the natural heart which varies with age and size between 30 and 100 cc.
A second condition is that the instantaneous flows are pulsatile, i.e. they pass through a maximum during each cycle and are then cancelled out.
A third imperative condition is that the charge loss on aspiration is always below a very low threshold of about 10 cm of water or 10 millibars so as to prevent haemolysis of the blood, whose pressure is reduced. Turbulence which may cause local pressure reductions must be prevented. It is better not to use valves which generate turbulence and whose unsatisfactory operation may have serious consequences.
Obviously another important condition is the complete operational reliability.
Preferably the flow pulsation frequency is the same as the normal pulse and can be easily varied to ensure the regulation of flows as a function of the requirements of the organism. Generally the frequency is regulated in such a way that it maintains an average constant pressure in the aorta.
Such a result can automatically be obtained by a cardiac pump driven by a motor having a constant torque. A pressure rise or fall automatically leads to an increase or decrease in frequency which re-establishes the pressure. Therefore the artificial heart will preferably be driven by a motor having a constant torque.
The documents referred to hereinbefore describe the different types of artificial heart on which experiments have hitherto been performed. None of them comprises a rotary plunger pump of trochoidal, i.e. epitrochoidal or hypotrochoidal shape.
Industrial motors and pumps having a trochoidal rotary plunger are known which are also designated by the name Wankel engines and comprise a cylindrical rotor and a body which defines one or more cylindrical cavities in each of which is placed a rotor, said cavities constituting sleeves or casings of the rotor when the latter is driven both in circular translation and in rotation about its centre.
The following patents describe such motors or pumps: French Pat. 2,250,892 (Gray); French Pat. 2,260,008 (Dornier); French Pat. 2,087,187 (Kaspers); French Pat. 1,166,192 (NSU); U.S. Pat. No. 3,221,664 (Jernaes); German Pat. 2,021,513 (Schultheis); British Pat. 1,350,728 (Dornier).
None of these patents describes the use of a rotary plunger pump of the trochoidal type as a cardiac pump for an artificial heart.
Moreover, the use of these pumps as artificial hearts can also not be gathered from earlier documents describing industrial pumps. A cardiac pump must be rotated at slow speed, i.e. the number of revolutions per minute must correspond to the pulse frequency varying, for example, between 60 and 180 r.p.m., whereas an industrial pump is driven at speeds of 1000 to 3000 r.p.m.
In industrial pumps a sealing defect between the rotor and the stator is partly compensated by the high speed dynamic entrainment of the fluid. In a cardiac pump the sealing between the rotor and the stator must be adequate at low speeds.
The rotor of a trochoidal cardiac pump is driven at uniform speed which is an important advantage for the construction of a drive motor.
To permit its use as a cardiac pump serving to replace the whole heart or half the heart, a trochoidal rotor pump must have two chambers with an admission opening and a discharge opening or four chambers whereof two are provided with an admission opening and two with a discharge opening, whereby said openings must have an adequate passage cross-section so as not to cause too large losses of charge. Moreover, the instantaneous flow from the discharge openings must be pulsatile.